Dual-Port SRAM Connection Structure

ABSTRACT

The present disclosure provides a static random access memory (SRAM) cell. The SRAM cell includes first and second inverters cross-coupled for data storage, each inverter including at least one pull-up device and at least two pull-down devices; at least four pass gate devices configured with the two cross-coupled inverters; at least two ports coupled with the at least four pass-gate devices for reading and writing; a first contact feature contacting first two pull-down devices (PD- 11  and PD- 12 ) of the first inverter; and a second contact feature contacting second two pull-down devices (PD- 21  and PD- 22 ) of the second inerter.

CROSS REFERENCE

This application is a Divisional of U.S. patent application Ser. No.14/814,242 filed Jul. 30, 2015, issuing as U.S. Pat. No. 9,773,545,which is a Divisional of Ser. No. 13/732,980 filed on Jan. 2, 2013entitled “DUAL-PORT SRAM CONNECTION STRUCTURE” (Attorney Docket No.2012-0467/24061.2212), now U.S. Pat. No. 9,099,172, the disclosures ofwhich are incorporated herein by reference.

BACKGROUND

In deep sub-micron integrated circuit technology, an embedded staticrandom access memory (SRAM) device has become a popular storage unit ofhigh speed communication, image processing and system-on-chip (SOC)products. For example, a dual port (DP) SRAM device allows paralleloperation, such as 1R (read) 1W (mite), or 2R (read) in one cycle, andtherefore has higher bandwidth than a single port SRAM. In advancedtechnologies with decreased feature size and increased packing density,low loading and high speed of the cell structure are important factorsin embedded memory and SOC products. Various gate structures areimplemented to achieve high packing density and high speed. For example,a U-shaped gate structure is employed in the SRAM structure. However,the U-shaped gate structure induces potential issues including pull-down(PD) device variation and integration concerns on fin-like field-effecttransistor (FinFET) structure. Furthermore, the critical dimensionuniformity (CM) in the U-shaped gate structure also introduces neckingand leakage problems. Accordingly, the U-shaped gate structure impactedthe SRAM cell stability and limited the scaling (or shrink) capability.It is therefore desired to have a new structure and method to addressthe above issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion,

FIG. 1 is a schematic view of a dual port static random access memory(DP SRAM) cell constructed according to various aspects of the presentdisclosure in one embodiment.

FIG. 2 is a schematic view of a DP SRAM cell constructed according tovarious aspects of the present disclosure in another embodiment.

FIG. 3 is a schematic view of a DP SRAM cell constructed according tovarious aspects of the present disclosure in another embodiment.

FIGS. 4, 5, 6, 7 and 9 are top views of a DP SRAM cell constructedaccording to various aspects of the present disclosure in oneembodiment.

FIG. 8 is a sectional view of an interconnect structure incorporated inthe DP SRAM cell structure of FIG. 7 constructed according to oneembodiment.

FIG. 10 is a top view of a DP SRAM cell constructed according to variousaspects of the present disclosure in various embodiments.

FIG. 11 is a top view of a DP SRAM cell constructed according to variousaspects of the present disclosure in various embodiments.

FIG. 12 is a top view of a DP SRAM cell constructed according to variousaspects of the present disclosure in various embodiments.

FIG. 13 is a sectional view of a DP SRAM structure having a pluralitycells constructed according to one embodiment.

FIG. 14 is a top view of a DP SRAM cell or a portion thereof constructedaccording to various aspects of the present disclosure in variousembodiments.

FIG. 15 is a schematic view of a DP SRAM structure constructed accordingto various aspects of the present disclosure in one embodiment.

FIG. 16 is a schematic view of a DP SRAM structure constructed accordingto various aspects of the present disclosure in another embodiment.

FIG. 17 is a schematic view of a DP SRAM structure constructed accordingto various aspects of the present disclosure in yet another embodiment.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting, Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 is a schematic view of a dual-port (DP) SRAM cell 100 constructedaccording to various aspects of the present disclosure in oneembodiment. In one embodiment, the DP SRAM cell 100 includes finfield-effect transistors (FinFETs). In another embodiment, the DP SRAMcell 100 includes planar field-effect transistors (FETs). The DP SRAMcell 100 includes first and second inverters that are cross-coupled. Thefirst inverter includes a first pull-up device formed with a p-typefield-effect transistor (pFET), referred to as PU-1. The first inverteralso includes a first plurality of pull-down devices formed with n-typefield-effect transistors (nFETs) and configured in parallel mode.Specifically, the drains of the first plurality pull-down devices areelectrically connected together, the corresponding sources areelectrically connected together, and the corresponding gates areelectrically connected together. The second inverter includes a secondpull-up device formed with a pFET, referred to as PU-2. The secondinverter also includes a second plurality of pull-down devices formedwith nFETs and configured in parallel mode. The number of the firstplurality of pull-down devices and the number of the second plurality ofpull-down devices are equal for a balanced cell structure. In oneembodiment, the first plurality of pull-down devices includes two nFETs,referred to as PD-11 and PD-12, respectively. In one embodiment, thesecond plurality of pull-down devices includes two nFETs, referred to asPD-21 and PD-22, respectively.

The drains of PU-1, PD-11 and PD-12 are electrically connected together,defining a first drain node (or first node). The drains of PU-2, PD-21and PD-22 are electrically connected together, defining a second drainnode (or second node). The gates of PU-1, PD-11 and PD-12 areelectrically connected and coupled to the second node. The gates of PU-2PD-21 and PD-22 are electrically connected and coupled to the firstnode. The sources of PU-1 and PU-2 are electrically connected to thepower line (Vcc line), The sources of PD-11, PD-12, PD-21, and PD-22 areelectrically connected to a complementary power line (Vss line). In oneembodiment of the DP SRAM cell layout, the sources of PD-11 and PD-12are electrically connected to a first Vss line while the sources ofPD-21 and PD-22. are electrically connected to a second Vss line.

The DP SRAM cell 100 further includes a first port (port-A) and a secondport (port-B). In one embodiment, the port-A and port-B include at leastfour pass-gate devices, referred to as PG-1, PG-2, PG-3 and PG-4,respectively. The port-A includes a first pass-gate device (PG-1) and asecond pass-gate device (PG-2). The port-B includes a third pass-gatedevice (PG-3) and a fourth pass-gate device (PG-4). The drain of PG-1 iselectrically connected to a first bit-line (referred to as A_BL). Thesource of PG-1 is electrically connected to the first node. The gate ofPG-1 is electrically connected to a first word-line (referred to asport-A WL). The drain of PG-2 is electrically connected to a firstbit-line bar (A_BLB). The source of PG-2 is electrically connected tothe second node. The gate of PG-2 is electrically connected to a firstword-line (port-A WL). The drain of PG-3 is electrically connected to asecond bit-line (B_BL). The source of PG-3 is electrically connected tothe first node. The gate of PG-3 is electrically connected to the secondword-line (port-B WL). The drain of PG-4 is electrically connected to asecond bit-line bar (B_BLB). The source of PG-4 is electricallyconnected to the second node. The gate of PG-4 is electrically connectedto the second word-line (port-B WL).

The cell 100 may include additional devices such as additional pull-downdevices and pass-gate devices. Specifically, the first inverter includesa number of pull-down devices configured in parallel similar to theconfiguration of PD-11 and PD-12. More specifically, the drains of thepull-down devices in the first inverter are electrically connectedtogether. The sources of the pull-down devices in the first inverter areelectrically connected together. The gates of the pull-down devices inthe first inverter are electrically connected together. The secondinverter includes the same number of pull-down devices configured inparallel similar to the configuration of PD-21 and PD-22 for balance.Specifically, the drains of the pull-down. devices in the secondinverter are electrically connected together. The sources of thepull-down devices in the second inverter are electrically connectedtogether. The gates of the pull-down devices in the second inverter areelectrically connected together.

The first port includes the first pass-gate device or a number of thefirst pass-gate devices (still referred to PG-1) configured in parallel.Specifically, the number of the first pass-gate devices are configuredsuch that the drains, sources and gates are electrically connectedtogether, respectively. More specifically, the drains of the firstpass-gate devices (PG-1) are electrically connected to a first bit-line(A_BL). The sources of PG-1 are electrically connected to the firstnode. The gates of PG-1 are electrically connected to a first word-line(port-A WL).

Similarly, the first port includes the second pass-gate device or thesame number of the second pass-gate devices (still referred to PG-2)configured in parallel. Specifically, the number of the second pass-gatedevices are configured such that the drains, sources and gates areelectrically connected together, respectively. More specifically, thedrains of PG-2 are electrically connected to a first bit-line bar(A_BLB). The sources of PG-2 are electrically connected to the secondnode. The gates of PG-2 are electrically connected to a first word-line(port-A WL).

The second port includes the third pass-gate device or the same numberof the third pass-gate devices (still referred to PG-3) configured inparallel. Specifically, the number of the third pass-gate devices areconfigured such that the drains, sources and gates are electricallyconnected together, respectively. More specifically, the drains of PG-3are electrically connected to a second bit-line (B_BL). The sources ofPG-3 are electrically connected to the first node. The gates of PG-3 areelectrically connected to the second word-line (port-B WL).

The second port includes the fourth pass-gate device or the same numberof the fourth pass-gate devices (still referred to PG-4) configured inparallel, Specifically, the number of the fourth pass-gate devices areconfigured such that the drains, sources and gates are electricallyconnected together, respectively. More specifically, the drains of PG-4are electrically connected to a second bit-line bar (B_BLB). The sourcesof PG-4 are electrically connected to the second node. The gates of PG-4are electrically connected to the second word-line (port-B WL).

In the present embodiment of the SRAM cell 100, the total number of theFETs in the cell is greater than 12.

FIG. 2 is a schematic view of a dual-port (DP) SRAM cell 102 constructedaccording to various aspects of the present disclosure in anotherembodiment. The SRAM cell 102 is similar to the SRAM cell 100 of FIG. 1but with different routing and configuration as illustrated in FIG. 2.

FIG. 3 is a schematic view of a dual-port (DP) SRAM cell 104 constructedaccording to various aspects of the present disclosure in yet anotherembodiment, The SRAM cell 104 is similar to one embodiment of the SRAMcell 100 in FIG. 1 where the number of the pull-down devices and thenumber of the pass-gate devices are more than four, In the SRAM cell104, the first inverter includes 6 pull-down devices PD-11, PD-12,PD-13, PD-14, PD-15 and PD-16. The second inverter includes 6 pull-downdevices PD-21, PD-22, PD-23, PD-24, PD-25 and PD-26. Additionally, theSRAM cell 104 includes 8 pass gate devices configured to form the firstand second ports. Specifically, the port-A includes 4 pass-gate devicesPG-11, PG-12, PG-21 and PG-22. The port-B includes 4 pass-gate devicesPG-31, PG-32, PG-41 and PG-42. The drains of PG-11 and PG-12 areelectrically connected to a first bit-line (A_(—) BL). The sources ofPG-11 and PG-12 are electrically connected to the first node. The gatesof PG-11 and PG-12 are electrically connected to a first word-line(referred to as port-A WL). The drains of PG-21 and. PG-22 areelectrically connected to a first bit-line bar (A_BLB). The sources ofPG-21 and PG-22 are electrically connected to the second node. The gatesof PG-21 and PG-22. are electrically connected to a first word-line(port-A WL). The drains of PG-31 and PG-32 are electrically connected toa second bit-line (B_BL). The sources of PG-31 and PG-32 areelectrically connected to the first node. The gates of PG-31 and PG-32are electrically connected to the second word-line (port-B WL). Thedrains of PG-41 and PG-42 are electrically connected to a secondbit-line bar (B_BLB). The sources of PG-41 and PG-42 are electricallyconnected to the second node. The gates of PG-41 and PG-42 areelectrically connected to the second word-line (port-B WL).

In the SRAM cell 104, the number of the pull-down devices is greaterthan the number of the pass-gate devices. Specifically, a ratio “R” isdefined as R=Npd/Npg where Npd is a number of the pull-down devices in aSRAM cell and Npg is a number of the pass gate devices in the SRAM cell.The ratio R is greater than 1 to increase sink current, access speed,and device reliability of the SRAM cell. The ratio R may be 3/2, 2, or5/4 in various examples. The total number of the nFETs and pFETs in thecell is greater than 12 such that the ratio R is tuned to be greaterthan 1. In the present embodiment illustrated in FIG. 3, the ratio R is3/2, and the total number of FETs is 22.

In one embodiment, the SRAM cell 104 (or 100 or 102) includes fin-likeactive regions and FinFETs with enhanced performance and increasedpacking density. Various n-typeFinFETs (nFinFETs) and p-type FinFETs(pFinFETs) may be formed by any proper technology. In one embodiment,the various nFinFETs and pFinFETs are formed by a process includingetching a semiconductor to form trenches, partially filling the trenchesto form shallow trench isolation (STI) features and fin active regions.In furtherance of the present embodiment, an epitaxy semiconductor layeris selectively formed on the fin active region. In another embodiment,the various FinFETs are formed by a process including depositing adielectric material layer on the semiconductor substrate, etching thedielectric material layer to form openings thereof, selective epitaxygrowing a semiconductor material (such as silicon) on the semiconductorsubstrate within the openings to form fin active regions and STIfeatures. In another embodiment, the various FinFETs may includestrained features for enhanced mobility and device performance. Forexample, the pFinFETs include epitaxy grown silicon germanium on asilicon substrate. For another example, the pFinFETs include epitaxygrown silicon carbide on the silicon substrate. In another embodiment,the various FinFETs are formed using high k/metal gate technology wherethe gate includes a gate dielectric having high k dielectric materialand a gate electrode having metal.

In the DP SRAM cell 100, 102 and 104 (collectively referred to as DPSRAM cell), various FETs are coupled by an interconnect structure havingcontacts, vias and metal lines. Especially, the DP SRAM cell includescontact features and/or via features designed and configured to addressthe issues discussed in the background. In one embodiment, the DP SRAMcell includes a long contact feature landing on and contacting gates oftwo or more pull-down devices. In furtherance of the embodiment, thegates of the pull-down devices are aligned in a first direction and thelong contact feature is aligned in a second direction perpendicular tothe first direction. In another embodiment, the contact featuresrespectively connecting the pass-gate devices are positioned in anasymmetric configuration. In furtherance of the embodiment, in an arrayof DP SRAM cells, the contact features associated pass-gate devices ofthe multiple cells are designed in a zigzag configuration. In yetanother embodiment, the DP SRAM cell includes a long self-alignedcontact feature oriented with two adjacent parallel gates andself-aligned between the two adjacent parallel gates. In yet anotherembodiment, the DP SRAM cell includes a zero via layer (Via-0 layer)vertically disposed between the contact layer and the first metal layer(M1 layer). The Via-0 layer includes various via features (Via-0features) to provide vertical connections between the contact featuresin the contact layer and the metal lines in the M1 layer for spaceenlargement and packing density enhancement. Various embodiments arefurther described below with reference to FIGS. 4 through 17.

FIG. 4 is a top view of a DP SRAM cell 110 constructed according tovarious aspects of the present disclosure in one embodiment. In oneembodiment, the DP SRAM cell 110 is a portion of the DP SRAM cell 100 ina particular configuration. The DP SRAM cell 110 includes one cell of aDP SRAM array and is formed on a semiconductor substrate. Thesemiconductor substrate includes silicon. Alternatively, the substrateincludes germanium, silicon germanium or other proper semiconductormaterials. The semiconductor substrate may include other proper featuresand structures. In one embodiment, the semiconductor substrate employs alayer of semiconductor material formed over an insulating layer on asupporting bulk wafer for isolation. The technology and structure arereferred to as semiconductor on isolation (SOI). The SOI structure canbe formed by different techniques including separation by implantedoxygen (RMOX), bonding and etching back (BESOT), and zone melting andrecrystallization (ZMR).

The DP SRAM cell 110 is formed in a unit cell region 112 of thesemiconductor substrate. The unit cell region 112 is defined by the unitcell boundary 114. In one embodiment, the unit cell region 112 isdefined in a rectangular shape spanning to a first dimension 116 in afirst direction and spanning to a second dimension 118 in a seconddirection perpendicular to the first direction. The first dimension 116is greater than the second dimension 118. The first and seconddimensions (116 and 118) are referred to as a long pitch and a shortpitch, respectively. In one embodiment, a SRAM array having a pluralityof cells is configured to form a two-dimensional periodic structure withperiodic constants as the long pitch and short pitch in the first andsecond directions, respectively. The first and second directions arealso referred to by numerals 116 and 118, respectively. The SRAM cell110 includes an N-well region 120 disposed in the central portion of thecell. The SRAM cell 110 further includes a P-well region 122 disposed onthe both sides of the N-well 120. In one embodiment, the N-Well 120 andP-well 122 are extended to multiple cells beyond the unit cell boundary.For example, the N-well 120 and P-well 122. are extended to 4 or morecells in the second direction. In another embodiment, the N-well 120 orP-well is not a continuous structure and may be defined in associatedactive regions.

Various active regions are defined in the substrate by isolationfeatures and are isolated from each other by the isolation features. Theisolation features are formed in the semiconductor substrate with aproper technology. In one embodiment, the isolation features are formedby a shallow trench isolation (STI) technique. In another embodiment,the isolation features are alternatively formed by a local oxidation ofsilicon (LOCOS) technique. In yet another embodiment, the formation ofthe STI features includes etching a trench in a substrate and fillingthe trench by one or more insulator materials such as silicon oxide,silicon nitride, or silicon oxynitride. The filled trench may have amulti-layer structure such as a thermal oxide liner layer with siliconnitride filling the trench. The active regions are defined in thesemiconductor substrate upon the formation of the isolation features. Inthe present embodiment, the FETs in the SRAM cell 110 are planartransistors formed in the planar active regions.

In one embodiment, the DP SRAM cell 110 includes a first active region124, a second active region 126, a third active region 128 and a fourthactive region 130 formed in the P-well 122. The DP SRAM cell 110 furtherincludes a fifth active region 132 and a sixth active region 134 formedin the N-well 120. The first active region 124 through the sixth activeregion 134 have elongated shapes and are oriented in the seconddirection and distributed along the first dimension. The first throughsixth active regions or a subset thereof may be extended to multiplecells, such as 4 or more cells in the second direction.

In each fin active feature, one or more pull-down device (PD), one ormore pass-gate device (PG), or a combination thereof can be formed.Particularly, each active feature includes one PD, one PG, two PDs, twoPGs, or PD/PG (one PD and one PG). in the present embodiment, thepass-gates PG-1 and PG3 are formed on the active region 124. Thepull-down devices PD-11 and PD-12 are formed on the active region 126.Similarly, for a balanced structure of the SRAM cell 110, the pass-gatesPG-2 and PG4 are formed on the active region 128. The pull-down devicesPD-21 and PD-22 are formed on the fin active region 130. As to thepull-up devices, the fifth and sixth active regions 132 and 134 aredisposed in the N-well 120, The pull-up device PU-1 is formed on thefifth active region 132. and the pull-up device PU-2 is formed on thesixth active region 134.

Various gate features (or gates) are formed within the DP SRAM cell 110for various nFETs and pFETs. A gate feature includes a gate dielectriclayer (such as silicon oxide) and a gate electrode (such as dopedpolysilicon) disposed on the gate dielectric layer. In anotherembodiment, the gate feature alternatively or additionally includesother proper materials for circuit performance and manufacturingintegration. For example, the gate dielectric layer includes high kdielectric material layer. The gate electrode includes metal, such asaluminum, copper, tungsten or other proper conductive material. Variousgates are oriented in the first direction 116 and configured with thevarious active regions to form respective pull-up devices, pull-downdevices and pass-gate devices.

In the present embodiment, a long gate 136 is disposed over the activeregion 126 and further extends over the fifth active region 132, formingPD-11 and PU-1, respectively. Similarly, another long gate 137 isdisposed over the active region 130 a and further extended over thesixth active region 134, forming PD-21 and PU-2, respectively. A shortgate 138 is disposed on the active region 126 and configured to formPD-12. Similarly, another short gate 139 is disposed on the activeregion 130 and configured to form PD-22. Other four gates 141, 142, 143and 144 are disposed on active regions 124 and 128, forming thepass-gate devices PG-1, PG-2, PG-3 and PG-4, respectively.

In the present embodiment, PD-11 and PD-12 share a first common drain,PD-21 and PD-22 share a second common drain, PG-1 and PG-3 share a thirdcommon drain and PG-2 and PG-4 share a fourth common drain.

In another embodiment of the configuration as illustrated in FIG. 4, thefirst active region 124 through the fourth active region 130 in theP-well 122 and the associated pull-down devices and pass-gate devicesare symmetrically disposed on the two sides of the N-well 120.

FIG. 5 illustrates a top view of the DP SRAM cell 110, includinginterconnect features. Various interconnect structures may be utilizedto couple the nFETs and pFETs to form the functional SRAM cell. Thosecontact features contacting active regions are also referred to asactive contact features. Those contact features contacting gates arealso referred to as gate contact features. In one embodiment, the SRAMcell 110 includes gate contact features 146-1, 146-2, 146-3 and 146-4landing on the gates 141, 142, 143 and 144, respectively. The SRAM cell110 also includes active contacts features 148 disposed on the activeregions 124, 126, 128, 130, 132 and 134 and directly landing on therespective active regions, as illustrated in FIG. 5. Particularly, thoseactive contact features contact sources, drains or common drains of therespective FETs. In the present embodiment, the active contact features148 have elongated shape and length dimensions are aligned in the firstdirection. The active contact features 148 are not individually labeledin FIG. 5 for simplicity. Only two exemplary ones are labeled out.Labeled as 148-1 is one of the active contact features 148 disposed onthe active region 126 between the gates 136 and 138. Labeled as 148-2 isone of the active contact features 148 disposed on the active region 130between the gates 137 and 139. Particularly, the active contact feature148-1 contacts the common drain of PD-11 and PD-12 and is furtherextended to the drain of PU-1. The active contact feature 148-2 contactsthe common drain of PD-21 and PD-22 and is further extended to the drainof PU-2.

Other contact features are present in the SRAM cell 110 and areillustrated in FIG. 6. Those other contact features are shown in FIG. 6(instead of in FIG. 5) only for understanding and clarification. It isnot mean that those other contact features are formed afterward.Particularly, in one embodiment, the contact features in FIG. 5 andother contact features newly presented are formed simultaneously in asame fabrication procedure. FIG. 6 illustrates a top view of the DP SRAMcell 110. The SRAM cell 110 includes one (or more) long gate contactfeature 150 configured to contact and connect adjacent gates. The longgate contact feature 150 has an elongated shape and its length spans inthe second direction while the adjacent gates are oriented in the firstdirection. In the present embodiment, the SRAM cell 110 includes longgate contact features 150-1 and 150-2, The long gate contact feature150-1 is configured to land on both gates 136 and 138 such that thegates 136 and 138 are electrically connected. By the long gate contactfeature 150-1, a U-shaped gate structure and the corresponding roundingissue are eliminated. Similarly, the long gate contact feature 150-2 isconfigured to land on both gates 137 and 139 such that the gates 137 and139 are electrically connected.

The SRAM cell 110 also includes one (or more) gate contact feature 152disposed in the N-well 120 and configured to contact a gate in theN-well 120. In one embodiment, the gate contact feature 152 has anelongated shape and the length dimension spans in the second direction.In the present embodiment, the SRAM cell 110 includes two gate contactfeatures 152-1 and 152-2. The gate contact feature 152-1 lands on andconnects to the gate 136. The gate contact feature 152-2 lands on andconnects to the gate 137. In one embodiment, the gate contact feature152 is configured to contact a gate and is extended to further contactan active region. For example, the gate contact feature 152-1 isconfigured to contact the gate 136 associated with PU-1 and is extendedin the second direction to further contact the drain of the PU-2.Similarly, the gate contact feature 152-2 is configured to contact thegate 137 associated with PU-2 and is extended in the second direction tofurther contact the drain of the PU-1. In another embodiment, the activecontact feature 148-1 is extended to be merged with the gate contactfeature 152-2 such that the corresponding features (the common drain ofPD-11 and PD-12, the drain of PU1 and the gate of PU-2) are electricallyconnected by the merged contact feature. In another embodiment,similarly, the active contact feature 148-2 is extended to be mergedwith the gate contact feature 152-1 such that the corresponding features(the common drain of PD-21 and PD-22, the drain of PU2 and the gate ofPU-1) are electrically connected by the merged contact feature.

The SRAM cell 110 further includes other interconnect featuresillustrated in FIG. 7 in a top view constructed according to variousembodiments. In one embodiment, the SRAM cell 110 includes a via zero(Via-0) layer below the first metal (M1) layer and disposed between thecontact layer and the M1 layer. The Via-0 layer includes various Via-0features 156 interposed between an underlying contact feature in thecontact layer and an overlying metal line in the M1 layer and contactsthe underlying contact feature and the overlying metal line. The Via-0layer is included in the SRAM cell 110 to provide space enhancement suchthat various features are properly coupled in a high packing layout.

The Via-0 layer and Via-0 features are further described with areference to FIG. 8 in a sectional view of an interconnect structure 160formed on a substrate 162. The substrate 162 includes various isolationfeatures (such as STI and labeled as “STI” in FIG. 8) formed therein anddefining various active regions separated from each other by theisolation features. Various gates (labeled as “gate”) are formed on theactive regions of the substrate 162. The interconnect structure 160includes contact features such as active contact features (labeled as“CO”) and gate contact features (labeled as “Gate_CO”). The activecontact features land on respective active regions and the gate contactfeatures land on respective gates.

The interconnect structure 160 also includes various metal layers, suchas the first metal layer (“M1”), the second metal layer (“M2”) and thethird metal layer (“M3”) successively disposed on the substrate 162 andvertically connected by via features in respective via layers, such asthe first via layer (“Via1”) between the MI and M2 layers and the secondvia layer (“Via2”) between the M2 and M3 layers.

Particularly, the interconnect structure 160 includes additionally a viazero layer (“Via-0”) disposed between the contact layer and M1 layer.The Via-0 features in the Via-0 layer are configured to contact theunderlying contact feature in the contact layer and the overlying metalline in the M1 layer. The Via-0 features in the Via-0 layer providespace enhancement such that contact features properly electricallyconnected with respective metal lines in the MI layer, especially in ahigh packing layout. For example, adjacent gates are close to eachother, leaving limited space between the adjacent gates. A contactfeature may have a small dimension in the top view such that the contactfeature is able to fit in the limited space. The corresponding Via-0feature may have a greater dimension to land on the underlying contactfeature and still have dimension large enough such that the overlyingmetal line is able to land on the Via-0 feature.

Referring back to FIG. 7, the SRAM cell 110 includes Via-0 features 156disposed on respective contact features. The Via-0 features 156 areshown in FIG. 7 as

that are similar to those for the contact features but are shadowed fordifferentiation. The Via-0 features 156 are not individually labeled inFIG. 7 for simplicity.

Referring to FIG. 9, the SRAM cell 110 further includes metal lines,such as metal lines 158 in the M1 layer to land on the respective Via-0features. The metal lines 158 are shown in FIG. 9 as rectangle withdashed lines for differentiation. The metal lines 158 are notindividually labeled in FIG. 9 for simplicity. The metal lines 158 mayhave an elongated shape. In one embodiment, the metal lines 158 areoriented in the first direction 116.

FIG. 10 is a top view of a DP SRAM cell 170 constructed according to oneor more embodiments. The DP SRAM cell 170 is similar to the DP SRAM cell110. The DP SRAM cell 170 includes pull-down devices (PD-11, PD-12,PD-21 and PD-22), pull-up devices (PU-1 and PU-2), and pass-gate devices(PG-1, PG-2, PG-3 and PG-4) configured to cross-coupled two invertersfor data storage and two ports for reading and writing. Particularly,the DP SRAM cell 170 includes one (or more) long gate contact feature150 configured to contact and connect adjacent gates. The long gatecontact feature 150 has an elongated shape and its length spans in thesecond direction 118 while the adjacent gates are oriented in the firstdirection. In the present embodiment, the SRAM cell 170 includes longgate contact features 150-1 and 150-2. The long gate contact feature150-1 is configured to land on the adjacent gates associated withpull-down devices PD-11 and. PD-12 such that the adjacent gates areelectrically connected. By the long gate contact feature 150-1, aU-shaped gate structure and the corresponding rounding issue areeliminated. Similarly, the long gate contact feature 150-2 is configuredto land on the adjacent gates associated with pull-down devices PD-21and PD-22 such that the adjacent gates are electrically connected. Inanother embodiment, the SRAM cell 170 includes Via-0 features disposedon respective contact features.

FIG. 11 is a top view of a DP SRAM cell 180 constructed according to oneor more embodiments. The DP SRAM cell 180 is similar to the DP SRAM cell110 that includes dual ports and long contact features designed to landon and connect two adjacent gates. The descriptions of similar featuresand configurations are not repeated here.

In the present embodiment, the DP SRAM cell 180 includes fin-like activefeatures 182. Accordingly, various pull-up devices, pull-down devicesand pass-gate devices in the DP SRAM cell 180 are FinFETs. FinFETs haveenhanced performance due to multiple gate coupling (referred to asdouble gate or triple gate) and have high packing density. Each activeregion may include one or more fin-like active features. In the presentembodiment, each active region for the pull-down devices and pass-gatedevices includes two fin-like active features. For example, the activeregion for the pull-down devices PD-11 and PD-12 includes two fin-likeactive features 182. Similarly, the active region for the pull-downdevices PD-21 and includes two fin-like active features 182. The activeregion for the pass-gate devices PG-1 and PG-3 includes two fin-likeactive features 182. The active region for the pass-gate devices PG-2and PG-4 includes two fin-like active features 182 as well.

The DP SRAM cell 180 includes pull-down devices (PD-11, PD-12, PD-21 andPD-22), pull-up devices (PU-1 and PU-2), and pass-gate devices (PG-1,PG-2, PG-3 and PG-4) configured to cross-coupled two inverters for datastorage and two ports for reading and writing.

Particularly, the DP SRAM cell 180 includes one or more) long gatecontact feature 150 configured to contact and connect adjacent gates.The long gate contact feature 150 has an elongated shape and its lengthspans in the second direction 118 while the adjacent gates are orientedin the first direction. In the present embodiment, the SRAM cell 180includes long gate contact features 150-1 and 150-2. The long gatecontact feature 150-1 is configured to land on the adjacent gatesassociated with pull-down devices PD-11 and PD-12 such that the adjacentgates are electrically connected. Similarly, the long gate contactfeature 150-2 is configured to land on the adjacent gates associatedwith pull-down devices PD-21 and PD-22 such that the adjacent gates areelectrically connected. As noted above, a U-shaped gate introducedrounding effect that degrades the gate quality. The rounding effect inthe FinFET structure is more severe because the FinFET structure is notplanar but 3-dimensional. By using the long contact feature 150 toconnect adjacent gates, the proper gate connection is achieved withoutusing U-shaped gate.

In another embodiment, the SRAM cell 180 includes Via-0 featuresdisposed on respective contact features. Each Via-0 feature contacts theunderlying contact feature in the contact layer and the overlying metalline in the M1 layer.

FIG. 12 is a top view of a DP SRAM cell 190 constructed according to oneor more embodiments. The DP SRAM cell 190 is similar to the DP SRAM cell110 in some aspects but has an asymmetric gate contact structure for thegate connections of the pass-gate devices. The descriptions of thesimilar features and configurations are not repeatedly for simplicity.The DP SRAM cell 190 includes pull-down devices (PD-11, PD-12, PD-21 andPD-22), pull-up devices (PU-1 and PU-2), and pass-gate devices (PG-1,PG-2, PG-3 and PG-4) configured to cross-coupled two inverters for datastorage and two ports for reading and writing. FIG. 12 only illustratesthe DP SRAM cell 190, in portion. For example, the active regions arenot shown for simplicity. The active regions may be similar to theactive regions of FIG. 10 (planar active regions) or the active regionsof FIG. 11 (fin-like active regions). Various interconnect features areshown in FIG. 12 and are further described below.

The SRAM cell 190 includes various contact features, via features andmetal lines. In one embodiment, the DP SRAM cell 190 includes one (ormore) long gate contact feature 150 configured to contact and connectadjacent gates. The long gate contact feature 150 has an elongated shapeand its length spans in the second direction 118 while the adjacentgates are oriented in the first direction. In the present embodiment,the SRAM cell 190 includes long gate contact features 150-1 and 150-2.The long gate contact feature 150-1 is configured to land on theadjacent gates associated with pull-down devices PD-11 and PD-12 suchthat the adjacent gates are electrically connected. By the long gatecontact feature 150-1, a U-shaped gate structure and the correspondingrounding issue are eliminated. Similarly, the long gate contact feature150-2 is configured to land on the adjacent gates associated withpull-down devices PD-21 and PD-22 such that the adjacent gates areelectrically connected. In another embodiment, the SRAM cell 190includes Via-0 features disposed on respective contact features.

Particularly, the SRAM cell 190 includes an asymmetric gate contactfeatures for the gate connections to the pass-gate devices. The SRAMcell 190 includes gate contact features 192-1, 192-2, 192-3 and 192-4configured to land on and contact the gates for the pass-gate devicesPG-1, PG-2, PG-3 and PG-4, respectively. The gate contact features192-1, 192-2, 192-3 and 192-4 are disposed in an asymmetricconfiguration. The gate contact features 192-1 and 192-3 are disposed ona first edge and the gate contact features 192-2 and 192-4 are disposedon a second edge. The first and second edges span in the first direction(X direction). The gate contact features 192-1 and 192-3 offset fromeach other in the first direction. Similarly, the gate contact features192-2 and 192-4 offset from each other in the first direction.

Specially, the gate contact features 192-1, 192-2, 192-3 and 192-4 arerespectively shared with adjacent cells. The asymmetric configuration ofthe gate contact features 192 of the pass-gate devices are furtherillustrated in FIG. 13 of a SRAM structure 200 in a top view. The SRAMstructure 200 includes exemplary four SRAM cells (Cell 1-1, Cell 1-2,Cell 2-1 and Cell 2-2), in portion, with cell boundaries illustrated indashed lines. Four gate contact features 202, 204, 206 and 208 aredisposed in the four cells to provide gate connections of the pass-gatedevices of the four SRAM cells. When looking from center to center ofthose gate contact features, the gate contact features 202, 204, 206 and208 are positioned in a zigzag configuration. If the SRAM cell in FIG.12 is the cell 2-2, the gate contact features 202 and 204 are the gatecontact features 192-4 and 192-2, respectively. More specifically, thegate contact feature 202 is disposed in the SRAM cell 2-2 and is sharedwith the SRAM cell 1-2 while the gate contact feature 204 is disposed inthe SRAM cell 1-2. and is share with the SRAM cell 2-2.

The pass-gate contact features 202-208 are disposed in a zigzagconfiguration through a plurality of SRAM cells. The pass-gate contactfeatures are zigzag configured and repeated along the second direction(Y direction). A third direction Z is defined as a directionperpendicular to the substrate (perpendicular to both X and direction).In one embodiment, such zigzag configuration is repeated along the Zdirection through via layers. The metal lines are similarly configuredto be aligned to the corresponding via features.

Referring back FIG. 12, the SRAM cell 190 further includes Via-0features configured to provide vertical connection between theunderlying contact features and the overlying metal lines in the M1layer for space enlargement.

The SRAM cell further includes first metal lines (“M1”) in the Ml layerand second metal lines (“M2”) in the M2 layer, configured to provideelectrical routing to the SRAM cell for various operations includingreading and writing. In the present embodiment, the first metal lines inthe M1 layer are oriented in the first direction (X direction) and thesecond metal lines in the M2 layer are oriented in the second direction(Y direction). The first metal lines are configured to verticallycontact the respective Via-0 features. The second metal lines (labeledas 196-1 through 196-9) are configured to connect to the first metallines through respective via features ((Via-1″) and further coupled tovarious inputs including power lines. For example, the second metal line196-5 is routed to the power line Vdd. In another example, the secondlines 196-4 and 196-6 are routed to the complimentary power line Vss.

FIG. 14 is a top view of a DP SRAM cell 210 constructed according to oneor more embodiments. The DP SRAM cell 180 includes pull-down devices(PD-11, PD-12, PD-21 and PD-22), pull-up devices (PU-1 and PU-2), andpass-gate devices (PG-1, PG-2, PG-3 and PG-4) configured tocross-coupled two inverters for data storage and two ports for readingand writing. The similar features and configurations in the DP SRAM cell210 are not repeated for simplicity.

In the SRAM cell 210, the various FETs to form pull-down devices,pull-up devices and pass-gate devices are formed using planar activeregions. In this case, a U-shaped gate structure is used with longself-aligned contact features to reduce various concerns including theissue associated with space limitation.

As illustrated in FIG. 14, two U-shaped gates 212 are formed anddisposed on the SRAM cell 210. A first U-shape gate 212-1 is disposed ona first portion (the right portion in this case) of the SRAM cell and asecond U-shape gate 212-1 is disposed on a second portion (the leftportion in this case) of the SRAM cell. Each U-shaped gate includesthree segments (first, second and third segments) connected together.The first and third segments are oriented in the first direction. Thesecond segment is oriented in a second direction. The second segmentdirectly connects to the first segment in one end and the third segmentin another end.

The first U-shaped gate 212-1 is disposed on the P-well 122 and thefirst segment is extended into the N-well 120. The first U-shaped gate212-1 forms a continuous gate for PD-11, PD-12 and PU-1. The secondU-shaped gate 212-2 is disposed on the P-well 122 and the first segmentof the U-shaped gate 212-2 is extended into the N-well 120. The secondU-shaped gate 212-2 forms a continuous gate for PD-21, PD-22 and PU-2.

Particularly, the DP SRAM cell 210 includes one or more longself-aligned contact features 214. The long self-aligned contactfeatures 214 are disposed on respective active regions and contact therespective active region. The long self-aligned contact features 214 areself-aligned between the respective gates. In the present embodiment,the SRAM cell 210 includes long self-aligned contact features 214-1 and214-2. Taking long self-aligned contact feature 214-1 as an example, thelong self-aligned contact feature 214-1 is oriented in the firstdirection and disposed between the gates for PG-1 and PG-3 that areparallel and oriented in the same direction. The long self-alignedcontact feature 214-1 further extends to between the two parallelsegments (first and third segments oriented in the first direction) ofthe long U-shaped gate 212-1. In one method to form the longself-aligned contact feature 214-1, an interlayer dielectric (ILD) layeris disposed on the gates and the substrate. An etch process is appliedto the ILD layer through en etch mask (such as patterned resist layer orhard mask). The etch process selectively etch the ILD material withoutetching the corresponding gates and therefore the contact trench isaligned with the active regions in the gaps between the parallel gates.Even though the openings defined in the etch mask are not fully alignedwith the active regions, due to the selective etch of the etch process,the contact trench is self-aligned with the active regions between theparallel gates (such as the active regions between the gates of the PG-1and PG-3).

In another embodiment when double patterning (or multiple patterning)technology is employed, the active contact trenches and gate contacttrenches are separately patterned. The etch process to etch the activecontact trench is tuned to selectively etch the ILI) material but notthe gate material (the top material layer on the gate is the gatepatterning hard mask the sidewall material layer is the gate spacer).Therefore, the long self-aligned contact feature 214-1 is self-alignedbetween the gate spacers and physically contacts the gate spacers.

In another embodiment, the SRAM cell 110 includes a via zero (Via-0)layer below the first metal (M1) layer and disposed between the contactlayer and the M1 layer, The Via-0 layer includes various Via-0 featuresinterposed between an underlying contact feature in the contact layerand an overlying metal line in the M1 layer and contacts the underlyingcontact feature and the overlying metal line, The Via-0 features enlargethe landing area such that the overlying metal lines easily land on andconnect the overlying self-aligned contact.

FIG. 15 is a top view of a SRAM structure 220 constructed according toone embodiment. The SRAM structure 220 includes a portion of aninterconnect structure disposed on a SRAM cell, such as the SRAM cell110. The SRAM structure 220 includes metal lines in a second metal layer(M2) and metal lines in the third metal layer (M3) and further includesvia features in the via layer between the M2 and M3 layers. The metallines in the M2 layer are oriented in the second direction (Y direction)and the metal lines in the M3 layer are oriented in the first direction(X direction), The metal lines in the M2 layer are respectivelyconnected to power lines (Vdd, Vss, or constant voltage lines such asVss or Vdd) and bit lines A-BLB, B_BLB, A-BL and B_Bl) as illustrated inFIG. 15. The metal lines in the M3 layer are respectively connected toword lines (WL-A and WL-B).

FIG. 16 is a top view of a SRAM structure 230 constructed according toone embodiment. The SRAM structure 230 includes a portion of aninterconnect structure disposed on a SRAM cell, such as the SRAM cell110. The SRAM structure 230 includes metal lines in a first metal layer(M1), metal lines in a second metal layer (M2) and metal lines in thethird metal layer (M3). In the present embodiment, a metal line 232 inthe M1 layer is connected to a power line Vdd and is oriented in thesecond direction (Y direction). Other metal lines in the M1 layer maypresent to provide cell local connections and landing pads. The metallines in the M2 layer are oriented in the second direction (Ydirection). The metal lines in the M2 layer are respectively connectedto power lines (Vdd, Vss,), shielding lines and bit lines (A-BLB, B_BLB,A-BL and B_Bl) as illustrated in FIG. 16. The metal lines in the M3layer are oriented in the first direction (X direction). The metal linesin the M3 layer are respectively connected to word lines (WL-A andWL-B).

FIG. 17 is a top view of a SRAM structure 240 constructed according toone embodiment. The SRAM structure 240 includes a portion of aninterconnect structure disposed on a SRAM cell, such as the SRAM cell110. The SRAM structure 240 includes metal lines in a first metal layer(M1), metal lines in a second metal layer (M2) and metal lines in thethird metal layer (M3). In the present embodiment, the metal lines 232in the M1 layer are respectively connected to power lines (Vdd and Vss)and are oriented in the second direction (Y direction). Other metallines in the M1 layer may present to provide cell local connections, Vsspower lines and landing pads. The metal lines in the M2 layer areoriented in the second direction (Y direction). The metal lines in theM2 layer are respectively connected to power lines (Vdd, Vss,),shielding lines and bit lines (A-BLB, B_BLB, A-BL and B_Bl) asillustrated in FIG. 17. The metal lines in the M3 layer are oriented inthe first direction (X direction). The metal lines in the M3 layer arerespectively connected to word lines (WL-A and WL-B).

In various embodiments, the disclosed DP SRAM device addresses variousissues noted in the background. The present disclosure provides adual-port SRAM cell and a layout with multiple pull-sown devices andmultiple pass-gate devices configured and coupled through variouscontact features according different embodiments. The disclosedstructure and layout are also good for high-k/metal-gate. One or moreother advantages may present in various embodiments. In one example, thelong gate contact features provide local connection to the adjacentgates with much great processing for lithography pattern. In anotherexample, the asymmetric gate contact features reduce the issue caused bycrowd space, which enhances the space and provides a layout suitable forcell shrinking and layout scaling in the advanced technology nodes. Inanother example, the fin active features are straight and some are longand continuous to form two FinFETs, such as pull-down devices and/orpass-gate devices, to provide a better device tracking/matching betweenthe pass-gate devices and pull-down devices on a wider range operationvoltage (from the highest to the lowest Vdd operation). In anotherexample, the simple shape of the active regions solves pull-down devicecurrent crowding issue as well as lithography proximity effect.

Various features and configurations in various embodiments may becombined to present in a SRAM cell. For example, a SRAM cell includes along gate contact to connect gates for PD-11 and PD-12 (another longgate contact feature to connect gates for PD-11 and PD-12 as well) andfurther includes an asymmetric gate contact features to contact thegates of the pass-gate devices. In another example, a SRAM cell includesa long gate contact to connect gates for PD-11 and PD-12 (another longgate contact feature to connect gates for PD-11 and PD-12 as well); anasymmetric gate contact features to contact the gates of the pass-gatedevices; and self-aligned contact features.

Thus, the present disclosure provides one embodiment of a static randomaccess memory (SRAM) cell that includes first and second inverterscross-coupled for data storage, each inverter including at least onepull-up device and at least two pull-down devices; at least fourpass-gate devices configured with the two cross-coupled inverters; atleast two ports coupled with the at least four pass-gate devices forreading and writing; a first contact feature contacting first twopull-down devices (PD-11 and PD-12) of the first inverter; and a secondcontact feature contacting second two pull-down devices (PD-21 andPD-22) of the second inerter.

The present disclosure also provides another embodiment of a staticrandom access memory (SRAM) cell structure that includes first andsecond inverters cross-coupled fir data storage, each inverter includingat least one pull-up device and at least two pull-down devices; at leastfour pass-gate devices (PG1, PG2, PG3 and PG4) configured with the twocross-coupled inverters; at least two ports coupled with the at leastfour pass-gate devices for reading and writing; and four contactfeatures (C1, C2, C3 and C4) contacting PG1, PG2, PG3 and PG4,respectively. The SRAM cell has an elongated shape oriented in a firstdirection, and C1, C2, C3 and C4 are configured such that each of C1,C2, C3 and C4 offsets with any others in the first direction.

The present disclosure also provides another embodiment of a staticrandom access memory (SRAM) cell that includes first and secondinverters cross-coupled for data storage. The first inverter includes afirst pull-up device (PU1) and two pull-down devices (PD-11 and PD-12)and the second inverter includes a second pull-up device (PU2) and othertwo pull-down devices (PD-21 and PD-22). The SRAM cell also includes afirst U-shaped gate physically connecting gate terminals of PD-11 andPD-12; a second U-shaped gate physically connecting gate terminals ofPD-21 and PD-22; a first long contact feature contacting a drain of PU1and a first common drain of PD-11 and PD-12; and a second long contactfeature contacting a drain of PU2 and a second common drain of PD-21 andPD-22.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A static random access memory (SRAM) cellcomprising: first and second inverters cross-coupled for data storage,wherein the first inverter includes a first pull-up device and twopull-down devices and the second inverter includes a second pull-updevice and two other pull-down devices; a first U-shaped gate physicallyconnecting gate terminals of the two pull-down devices; a secondU-shaped gate physically connecting gate terminals of the two otherpull-down devices; a first long contact feature contacting a drain ofthe first pull-up device and a first common drain of the two pull-downdevices; and a second long contact feature contacting a drain of thesecond pull-up device and a second common drain of the two otherpull-down devices.
 2. The SRAM cell of claim 1, further comprising fourpass-gate devices configured with the first and second cross-coupledinverters, wherein the four pass-gate devices include first, second,third and fourth pass-gate devices, respectively; and two ports coupledwith the four pass-gate devices for reading and writing, wherein thefirst long contact feature contacts a third common drain of the firstand third pass-gate devices, and the second long contact featurecontacts a fourth common drain of the second and fourth pass-gatedevices.
 3. The SRAM cell of claim 1, further comprising a via layerbelow a first metal layer, wherein the via layer includes a first viafeature directly contacting the first long contact feature and a firstmetal line in the first metal layer; and a second via feature directlycontacting the second long contact feature and a second metal line inthe first metal layer.
 4. The SRAM cell of claim 1, wherein the SRAMcell has an elongated shape oriented in a first direction, and the firstand second long contact features are oriented in the first direction. 5.The SRAM cell of claim of claim 4, wherein the first U-shaped gateincludes first, second and third segments, wherein the first and thirdsegments are oriented in the first direction, the second segment isoriented in a second direction perpendicular to the first direction, andthe second segment directly connects to the first segment in one end andthe third segment in another end; and the first long contact feature isself-aligned between the first and third segments.
 6. A static randomaccess memory (SRAM) cell comprising: first and second inverterscross-coupled for data storage, wherein the first inverter includes afirst pull-up device and two pull-down devices and the second inverterincludes a second pull-up device and two other pull-down devices; aU-shaped gate physically connecting gate terminals of at least one ofthe two pull-down devices and the two other pull-down devices, whereinthe U-shaped gate includes a first segment, a second segment, and athird segment, wherein the first and the third segments are oriented ina first direction and are parallel to each other, and wherein the secondsegment is oriented in a second direction perpendicular to the firstdirection; a long contact feature oriented in the first direction anddisposed between gates of two pass-gate devices, wherein the gates ofthe two pass-gate devices are parallel to each other and oriented in thefirst direction, and wherein the long contact feature further extendsbetween the first and third segments of the U-shaped gate.
 7. The SRAMcell of claim 6, further comprising: at least four pass-gate devicesconfigured with the cross-coupled first and second inverters; a firstelongated contact feature extended in the second direction, the firstelongated contact feature directly contacting adjacent gates extended,in the first direction perpendicular to the second direction, of the twopull-down devices of the first inverter; a second elongated contactfeature extended in the second direction, the second elongated contactfeature directly contacting adjacent gates extended, in the firstdirection perpendicular to the second direction, of the two pull-downdevices of the second inverter; and four contact features contacting theat least four pass-gate devices, respectively.
 8. The SRAM cell of claim7, wherein the SRAM cell has an elongated shape oriented in the firstdirection, and the four contact features are configured such that eachof the four contact features is offset from one another in the firstdirection.
 9. The SRAM cell of claim 7, wherein the SRAM cell spans afirst dimension from a first edge to a second edge in the firstdirection and a second dimension in the second direction; the seconddimension is less than the first dimension; a first pair of the fourcontact features are disposed at the first edge and are spaced from eachother in the first direction; a second pair of the four contact featuresare disposed at the second edge and are spaced from each other in thefirst direction.
 10. The SRAM cell of claim 7, wherein the at least fourpass-gate devices include first, second, third and fourth gates,respectively; the first, second, third and fourth gates each has anelongate shape oriented in the first direction; and the four contactfeatures contact the first, second, third and fourth gates,respectively.
 11. The SRAM cell of claim 7, wherein the four contactfeatures are connected to word lines.
 12. The SRAM cell of claim 6,further comprising: another U-shaped gate physically connecting gateterminals of the other of the at least one of the two pull-down devicesand the two other pull-down devices, wherein the another U-shaped gateincludes a fourth segment, a fifth segment, and a sixth segment, whereinthe fourth and the sixth segments are oriented in the first directionand are parallel to each other, and wherein the fifth segment isoriented in the second direction perpendicular to the first direction.13. The SRAM cell of claim 7, wherein: the first elongated contactfeature contacts a drain of the first pull-up device of the firstinverter and a first common drain of the two pull-down devices of thefirst inverter; the second elongated contact feature contacts a drain ofthe second pull-up device of the second inverter and a second commondrain of the two pull-down devices of the second inverter; the SRAM cellhas an elongated shape oriented in the first direction; and the firstelongated contact feature is disposed between the first and thirdsegments.
 14. A static random access memory (SRAM) cell comprising:first and second inverters cross-coupled for data storage, wherein thefirst inverter includes a first pull-up device and two pull-down devicesand the second inverter includes a second pull-up device and two otherpull-down devices; at least four pass-gate devices; at least two portscoupled with the at least four pass-gate devices to read and write; afirst U-shaped gate physically connecting gate terminals of the twopull-down devices; and a second U-shaped gate physically connecting gateterminals of the two other pull-down devices.
 15. The SRAM cell of claim14, wherein the two pull-down devices of the first inverter include afirst pull-down device and a second pull-down device having a first gateand a second gate, respectively; the two other pull-down devices of thesecond inverter include a third pull-down device and a fourth pull-downdevice having a third gate and a fourth gate, respectively; a firstelongated contact feature directly contacts the first and second gates;and a second elongated contact features directly contacts the third andfourth gates.
 16. The SRAM cell of claim 15, wherein the first andsecond pull-down devices of the first inverter have a first commondrain; and the third and fourth pull-down devices of the second inverterhave a second common drain.
 17. The SRAM cell of claim 16, wherein thefirst, second, third and fourth gates are elongated and extended in thefirst direction,
 18. The SRAM cell of claim 17, further comprisingactive regions that are elongated and extended in the second direction,wherein the active regions include a first active region that isunderlying the first gate and the second gate; and a second activeregion that is underlying the third gate and the fourth gate.
 19. TheSRAM cell of claim 18, wherein the active regions further include athird active region approximate to the first active region; a fourthactive region approximate to the second active region; first and secondpass-gate devices of the at least four pass-gate devices are formed onthe third active region; and third and fourth pass-gate devices of theat least four pass-gate devices are formed on the fourth active region.20. The SRAM cell of claim 19, wherein the SRAM cell has an elongatedshape that spans a first dimension in the first direction and a seconddimension in the second direction; the first dimension is greater thanthe second dimension; and the first, second, third and fourth activeregions are disposed along the first dimension such that the first andsecond active regions are between the third and fourth active regions.